php error line 24 createFromFormat

Hi,
I just downloaded this plugin and I REALLY want to use it, but I can’t upload a file for some reason. It keeps giving me this error:

Fatal error: Call to undefined method DateTime::createFromFormat() in /memphis-documents-library/mdocs-upload.php on line 24

After this happened the first time I changed the default timestamp to something closer to our own system, but it still didn’t upload.

I also want to mention that this is an internal network, and all IP addresses other than our company addresses are blocked. Should that cause a problem?

Also, is there a file size limit to the uploads?

Thanks so much!

https://ww.wp.xz.cn/plugins/memphis-documents-library/